bug#60897: 29.0.60; vc-revert fails to revert buffer

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Cc: epg@pretzelnet.org,  60897@debbugs.gnu.org
> Date: Tue, 24 Jan 2023 19:46:51 +0200
> 
> > How about replacing string= in these two cases with something smarter,
> > which would expand-file-name?  Comparing file names as simple strings
> > is wrought with trouble anyway.
> 
> This works as well:
> 
> diff --git a/lisp/vc/vc-dispatcher.el b/lisp/vc/vc-dispatcher.el
> index e1a3eff448d..8a0cdef4726 100644
> --- a/lisp/vc/vc-dispatcher.el
> +++ b/lisp/vc/vc-dispatcher.el
> @@ -608,7 +608,7 @@ vc-resynch-window
>  difference between the buffer and the file is due to
>  modifications by the dispatcher client code, rather than user
>  editing!"
> -  (and (string= buffer-file-name file)
> +  (and (string-prefix-p file buffer-file-name)
>         (if keep
>  	   (when (file-exists-p file)
>  	     (when reset-vc-info
> @@ -643,7 +643,7 @@ vc-resynch-buffers-in-directory
>  
>  (defun vc-resynch-buffer (file &optional keep noquery reset-vc-info)
>    "If FILE is currently visited, resynch its buffer."
> -  (if (string= buffer-file-name file)
> +  (if (string-prefix-p file buffer-file-name)
>        (vc-resynch-window file keep noquery reset-vc-info)
>      (if (file-directory-p file)
>  	(vc-resynch-buffers-in-directory file keep noquery reset-vc-info)

I'm confused: I though the problem was that FILE was some relative
form of buffer-file-name, which is why you wanted to run it through
expand-file-name, to make it absolute.  But if this is the case,
i.e. you have file = "foo" and buffer-file-name = /path/to/foo, then
string-prefix-p will not do the job, right?  And even if it did, you
could have false positives.

Maybe I just don't understand what this if clause is trying to test?